1. Description of the Field of the Invention
This invention describes additives for processing polyvinyl chloride compounds. The present invention is particularly concerned with calendering operations concerning such polyvinyl chloride compounds.
2. Description of the Art Practices
This invention, as previously noted, relates to the processing of polyvinyl chloride compounds. In particular, this invention is concerned with polyvinyl chloride compounds which are formed utilizing as a primary stabilizer organo-tin materials. It has been found necessary to utilize stabilizers in polyvinyl chloride products to scavenge hydrochloric acid which is formed by the thermal degradation of the polymer. The scavenged acid is converted by the organo-tin compound to the corresponding tin salt. The need to scavenge the hydrochloric acid arises because it further degrades the polyvinyl chloride product and in the absence of a scavenger, the rate of degradation is greatly accelerated by the presence of the hydrochloric acid. It has been found that the esters used herein provide low viscosity in processing of the melted polyvinyl chloride with no observable lower threshold on the amount of ester employed. That is, ordinarily internal lubricants do not function at less than 0.5 percent by weight of the polyvinyl chloride but that the present invention employes an ester which does reduce viscosity at lower concentrations.
Certain work concerning the partial esters of pentaerythritol for use in polyvinyl chloride resins is described in U.S. Pat. No. 4,220,570 issued Sept. 2, 1980 to Worschech et al.
Throughout the specification and claims, percentages and ratios are by weight and tempertures are in degrees Celsius unless otherwise noted. The terms pentaerythritol, tetrakis (hydroxymethyl) methane, and 2,2-bishydroxymethyl-1,3-propanediol are used interchangeably herein.